#include <bits/stdc++.h>
#define endl '\n'
#define ld long double
#define pb push_back
#define pf push_front
#define mod 998244353
#define se second
#define fi first
#define all(ls) (ls).begin(),(ls).end()
#define int long long
using namespace std;
int n,m;
const int N=2e5+10;
pair<int,int>a[N];
int f(int x){
queue<pair<int,int>>q;
q.push({1,x});
set<int>inds;
for(int i=0;i<n;i++)
if(i!=x)
inds.insert(i);
while(q.size()){
pair<int,int>u=q.front();
q.pop();
if(a[x].fi<=a[u.se].se-m)
return u.fi;
if(inds.empty())
continue;
vector<int>r;
for(int v:inds)
if(a[u.se].fi<=a[v].fi and a[v].fi<=a[u.se].se){
q.push({u.fi+1,v});
r.pb(v);
}
for(int v:r)
inds.erase(v);
}
return 1e9;
}
void solve(){
cin>>n>>m;
for(int i=0;i<n;i++){
cin>>a[i].fi>>a[i].se;
if(a[i].fi>a[i].se)
a[i].se+=m;
}
sort(a,a+n);
int ans=1e9;
for(int i=0;i<n;i++)
ans=min(ans,f(i));
if(ans==1e9)
ans=-1;
cout<<ans<<endl;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t=1;
// cin>>t;
for(int i=1;i<=t;i++){
// cout<<"Scenario #"<<i<<":"<<" ";
solve();
}
}
